Coupling PC-based commodity technology with distributed computing methodologies provides an important advance in the development of single-user dedicated systems. Beowulf is a class of experimental parallel workstations developed to evaluate and characterize the design space of this new operating point in price-performance. A key factor determining the realizable performance under real-world workloads is the means devised for interprocessor communications. A study has been performed to characterize the design parameters of a family of interconnect topoligies feasible with low cost mass market network technologies. Findings are presented which compare the advantage of complex segmented topologies over earlier parallel ``channel bonded'' schemes. Behavior sensitivities to packet size and traffic density are determined. It is shown that under many circumstances the more complex topologies result in better performance, and under favorable circumstances software routing techniques experience little performance degradation when compared to more expensive hardware switch mechanisms.